The latter also require Congress authorization, in a sense that the state is not allowed to create them without Congress "consenting" (e.g. via legislation):

"No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay."

But the Congress only has the power to grant or withhold such authorization; control still remains with the state. And, of course, the states can still have their militias - so long as the state does not explicitly organize them, it's not "keeping troops".